In a motor vehicle with an internal combustion engine a throttle valve is generally used to regulate a quantity of air delivered to the internal combustion engine. In order to suitably position the throttle valve, for example in the induction pipe of the internal combustion engine, the position of the throttle valve can be adjusted using a suitable drive. Hitherto mainly electric motors, for example in the form of direct current motors with brushes, have been used as possible drives.
For example, because of their better efficiency or their smaller size, so-called brushless direct current motors (BLDC motors) should be used in electrical throttle flap adjusting units in the future. Such motors are sometimes also referred to as electrically commutated electrical machines. The actuation means for such a BLDC motor should generally be arranged such that the motor is operated with optimum efficiency wherever possible. The actuation means can however respond very sensitively for example to parameter fluctuations and angular errors between a rotor and a stator of the motor. In this case an angular error is a deviation between an actual rotor position and a rotor position assumed by the control software.
For precise actuation of a BLDC motor it therefore appeared necessary hitherto to determine the current position of the rotor very accurately, for example using an angle transducer. Alternatively, the rotor position can be determined by means of a current-based angle detection. With current-based angle detection, the position of the rotor is calculated or estimated from the measured currents using an algorithm based on a motor model. Such current-based angle detection can sometimes be achieved because current regulation is often provided as a secondary control loop for revolution rate or torque regulation of the BLDC motor. Current regulation requires a current sensing means for detecting the actual current values.
For cost reduction, neither a current sensing means, and thus also no current regulation, should be provided in future throttle flap adjusting units nor should an additional angle transducer be disposed on the motor shaft. Instead the current position of the rotor should be detected indirectly using an already present throttle valve angle transducer that is provided to measure the current angular position of the throttle valve and that is for example connected to the shaft of the BLDC motor by means of a gearbox.
A generally non-linear relationship between a rotor position and an output voltage of the throttle valve angle transducer can for example be represented as a characteristic. Said characteristic is initially unknown and can for example be determined before the actual setting to work of the electrical throttle flap adjusting unit. For example, the characteristic can be determined automatically by a software-controlled process, which is also referred to as basic adaptation. One such possible process is described in DE 10 2009 063 326 A1. A result of the basic adaptation, i.e. the characteristic, can then be stored in a control unit (ECU) and subsequently used for the actuation of the BLDC-motor.
However, the relationship between the rotor position and the output voltage of the throttle valve angle transducer that was originally determined and stored as a characteristic can for example be changed during a subsequent operation by external influences, in particular by temperature fluctuations, and over the operating life, in particular by wear and tear. The originally adopted characteristic can then deviate from the currently prevailing relationship between the rotor position and the output voltage of the throttle valve angle transducer, so that the actuation of the BLDC motor can be erroneous.